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Magnesium Extraction From Magnesium Oxide Using Solid
Oxide Membrane Process
Rachel DeLucas, Marko Suput, Soobhankar Pati, and Uday Bhanu Pal
Boston University
Solid Oxide Membrane (SOM) Process for Magnesium Production-Leading to Magnesiothermic
Production of Other Metals
H2(g) + O2–(YSZ) →→→→ H2O(g) + 2e–
DC
Solid-Oxide Oxygen Ion Conducting Membrane(YSZ)
Anode
O2–(melt) →→→→ O2–
(YSZ)
Ionic Melt with Dissolved MgO
Mg2+(melt) + 2e– →→→→ Mg (g)
Cathode
CO(g) + O2–YSZ ���� CO2(g) + 2e–
V
O2–
O2–
Mg(g) + MeO = Me + MgO(s)
O2- →→→→ ½ O2(g) + 2e
Equivalent Circuit of SOM Cell
RRYSZYSZ(i(i)) RRfluxflux
(i(i)) RRmtmt EENernstNernst
RRYSZYSZ(e)(e) RRfluxflux
(e(e))
RRexternalexternalEEAppliedApplied IIcellcell
Rtotal = RYSZ (i) + Rflux
(i) + Rexternal + Rmt
EApplied - IcellRTotal = ENernst= (RT/4F) ln (PO2a/PO2
c)
Vertical Cross Section of the SOM Cell
Te
mp
era
ture
Experimental Setup
1 cm 3 cm
Potentiodynamic Sweep at 13000C
MgO Dissociation
0123456789
10
0 1 2 3 4 5
Applied Potential (Volts)
Cur
rent
(am
ps)
MgO Dissociation
SOM Electrolysis of MgO
0
1
2
3
4
5
6
7
8
9
0 1 2 3 4 5 6
Time (hours)
Cur
rent
(A
mps
)Potentiostatic Hold at 4.0 Volts
MgO concentration is decreasing
1150 oC
SOM Electrolysis of MgO20 KV scan( 2-4 micron penetration)
Energy (KeV)
0.0 0.5 1.0 1.5 2.0
CP
S
0
100
200
300
400
500
Mg
OC
Condensed Magnesium
Morphology of Magnesium Deposit
660 oC
530 oCCrystals
Lump
Stability of Membrane
100 µµµµm100 µµµµm100 µµµµm 100 µµµµm100 µµµµm100 µµµµm
a) As Receiveda) As Received b) Afterb) After ExperimentExperiment
••Membrane virtually unaffected after the 20 hour experimentMembrane virtually unaffected after the 20 hour experiment
••Selection of flux is critical to the processSelection of flux is critical to the process
••The operating life of Zirconia membrane will dominate overall cThe operating life of Zirconia membrane will dominate overall cost of ost of
the processthe process
SOM design with single tube arrangement (100-200 g/day)
Cylinder Geometry 1-tube Model Current Density
SOM Design With Triple Tube Arrangement (0.5-1kg/day)
Cylinder Geometry 3-tube Model Current Density
3613464Electrolyte Capacity (g)
4.121.778Minimum Anode-Cathode Separation
Distance (cm)
364.8130.7Active Cathode Area (cm2)
15.245.461Crucible ID (cm)
91.230.4Active Anode Area(cm2)
155Total active anode length (cm)
31No of Anodes
Tubular COE Tubular COEAnode Structure
0.5-1 Kg/day 100-200 g/daySpecifications
SOM Reactor Design for Mg Production
Top and Side Views of the Possible Scale-up Version of the
SOM Electrolytic Cell.
Steel Cathode
SOM Anode
Mg Vapor
Comparison of the SOM Process Versus State-of-the-art Process for Electrolytic Production of Magnesium
SOM Process
MgO
Mg(OH)2 Kiln CalcinationMgO
Mg
H2O+CO2
SOM Cell Physical Parameters
675-800 C1100-1150 COperating Temperature
Al2O3-SiO2MgO BasedRefractory
20-90 MT20 MTElectrolyte Capacity
Not Available290 cmCell Internal Diameter
3-6 cm4-8 cmAnode-Cathode Distance
Plate SteelPlate SteelCathode
0.5-100 kg/MT3-6 monthsHeat Anode Life/Consumption
Not Available185,900 cm2Anode Area
Not Applicable16 cmAnode Tube Diameter
100-120 cm100 cmWorking Length
Not Available37Number of Anodes
Chlorine and Chlorinated hydrocarbons
(CO, H2O or O2)By-Product Anode Gas
Graphite PlateTubular YSZAnode Structure
MgCl2MgOFeed Material
MgCl2 (1-4 MT/day)SOM (2 MT/day) Output
SOM Cell Operating Parameter Comparison
0.25V0.25VContact and Leads
0.3V0.3 VCathode
10-1610-12Specific Power (k Whr/kg)
0.7 V0.7 VAnode
Not Applicable1.3 ViR drop (YSZ, 2mm thick)
1.3 V1-2 ViR drop (Electrolyte)
2.75 V0.82 VDissociation Potential
Potential Drops
4.5-7.2 V4.4-5.4 VCell Voltage
0.4-0.7 Amp/cm21 Amp/cm2Current Density
Output
MgCl2 (1-4 MT/day)SOM (2 MT/day)
Comparison of Projected Energy Balance
1,303,4833,947,340Total Heat Consumed
495,646700,500Heat Losses (Top Lid, Walls, Floor, Anode Heads)
14,01665,678Heat Loss Cell/Carrier Gas
10,418157,344Heat Escaping with Anode Gas
80,814---------Heat in Spent Electrolyte
22,175596,116Heat Escaping with Mg
9,12112,000Impurity Decomposition
671,2932,061,786MgO Decomposition
--------------353,916Heating of raw material
Energy Sinks
1,303,4833,947,340Total Sources
154,682------------Pre-Melted Feed Material
-----------379,070Chem. Energy-anode feed
1,148,8013,568,270DC Electrical Energy
MgCl2 (0.62 MT/day)
k J/hr
SOM (2 MT/day) k J/hr
Energy Sources
SOM Features
• Cost Effective & Environmentally friendly– Direct reduction of Magnesium oxide– Minimize pre-processing, reduce capital and
operating cost
• High Current Density ( >1 Amp/cm2) � Good Scale up Potential
• Specific Energy consumption of MgO reduction is 10 KWh/Kg
Acknowledgements
Department of Energy
Boston University